Josh Marvil (CASS)

Josh Marvil Colloquium: Radio Continuum from Local Galaxies

Marsfield Lecture Theatre

Abstract

Title: Radio Continuum from Local Galaxies

Abstract: I will present the results of a two-part investigation into the radio continuum of
local galaxies, the purpose of which is to better understand how
spectral features are related to physical conditions and star
formation activity. First, I measure the integrated radio spectra for
250 local galaxies and determine that the average shape is better
described by a function with concave curvature than with the standard
power law model. I also investigate relationships between the radio
spectra and other aspects of the sources using a set of radio, far-IR
and optical properties. Second, I form over 30 high-resolution images
of two starbursting galaxies, M82 and NGC 2146, using observations
with the Karl G. Jansky Very Large Array (VLA) at frequencies from 1
to 46 GHz. I detect substantial variations in the radio spectrum
across the face of each galaxy, which I use to demonstrate that the
integrated spectrum is a composite of diverse spectral shapes. I
separate the resolved radio emission into thermal and nonthermal
components and develop a multi-zone description, with
elements including a star-forming disk and galactic wind. I
find evidence for spectral curvature in the synchrotron emission from
these objects, and compare these findings to models of
energy-dependent cosmic ray cooling as well as the predictions from
calorimeter models of the radio-farIR relation. Additionally, I
analyze filamentary emission detected in my very high resolution VLA
image of the galaxy M82 and discuss this emission in the context of
wind outflow channels and magnetic structures.